1. Technical Field
The present invention relates to an apparatus configured to detect reduction in insulation resistance between a vehicle body and a high-voltage circuit.
2. Related Art
A formerly known vehicle including a high-voltage battery system including a high-voltage circuit, such as a hybrid vehicle or an electrical vehicle, is equipped with an apparatus which detects reduction in insulation resistance between a vehicle body and the high-voltage circuit, for ensuring safety of occupants or the like (see, for example, Japanese Patent No. 3781289).
The apparatus disclosed in Japanese Patent No. 3781289 adopts a technique for detecting insulation deterioration between the vehicle body and the high-voltage circuit on the basis of a change in magnitude of a potential to ground at a first terminal of a coupling capacitor, which is in turn electrically connected to the high-voltage circuit at a predefined point of the high-voltage circuit via a second terminal of the coupling capacitor, during application of an AC voltage of predetermined frequency to the first terminal of the coupling capacitor through a predetermined output impedance.
To remove high-voltage noise generated in the high-voltage circuit, the apparatus disclosed in Japanese Patent No. 3781289 includes an analog filter, such a bandpass filter or a highpass filter, electrically connected between the first terminal of the coupling capacitor and a determiner that determines reduction in insulation resistance between the vehicle body and the high-voltage circuit.
In the apparatus disclosed in Japanese Patent No. 3781289, the analog filter is used for removing high-voltage noise generated in the high-voltage circuit. However, since various properties of the analog filter may alter due to, for example, a temperature variation and aging degradation and the like of each of elements constituting the analog filter, the accuracy of detecting insulation resistance between the vehicle body and the high-voltage circuit is inevitably low. To improve the detection accuracy, a temperature-compensated element may be included additionally in the analog filter. This however may lead to a more complicated configuration of the filter circuit and thus to increased cost.
In addition, since the high-voltage noise generated in the high-voltage circuit may be applied to the determiner, as a microcomputer or the like, configured to determine the reduction in insulation resistance, via the first terminal of the coupling capacitor that is a measurement point of the potential to ground, a protection circuit formed of high voltage-resistance elements may be provided to protect the determiner. This may lead to further increased cost.
In consideration of the foregoing, it would therefore be desirable to have an apparatus capable of improving accuracy of detecting reduction in insulation resistance between a vehicle body and a high-voltage circuit while ensuring high voltage resistance with a simpler configuration.